Is there bogwood in the tank that the babies are in?? as wood helps with there digestion, i feed my bristlenose fry algae wafers and had no problems. Water changes of 10-15% every other day are ideal as the babies will eat til the cows come home therefore produce loads of waste. Fry are very sensitive to high levels and nitrite levels. I usually leave my fry in with dad for 2 weeks and then raise them else where (after 2 weeks they leave the cave and scatter everywhere)

Could be a genetic defective gene that maybe 1 or both parents are carrying OR dietery problem (bristlenoses eat alot of green algae)